1. Field of the Invention
The present invention concerns novel block copolymers and a novel method for preparing polymers (preferably (meth)acrylate polymers and copolymers) having a narrow molecular weight distribution by metal-free anionic polymerization in the presence of a phosphonium cation.
2. Discussion of the Background
In the last decade, great interest has emerged concerning the polymerization of (meth)acrylates, particularly methyl methacrylate (MMA), under ambient conditions. A number of new polymerization systems have been reported, and a recent review covers most of the literature on the polymerization of MMA at ambient temperatures..sup.1 FNT .sup.1 Davis, T., Haddleton, D., Richards, S. J.M.S.-Rev. Macromol. Chem. Phys. 1994, C34, 243.
For example, a process known as Group Transfer Polymerization (GTP), introduced in the early 1980's, produced poly(methyl methacrylate) (PMMA) and allowed control of molecular weight distribution (MWD), molecular weight and molecular architecture at ambient temperatures..sup.2 Initially, coordinating ligands (.mu.-type ligands) such as metalated alkoxides.sup.3 and lithium chloride.sup.4 were utilized in the anionic polymerization of MMA. However, control of the MWD was lost at temperatures of .gtoreq.-40.degree. C. Thus, anionic polymerization in the presence of coordinating ligands was limited to temperatures of &lt;-40.degree. C. FNT .sup.2 (a) Webster, O., Hertler, W., Sogah, D., Farnham, W., and RajanBabu, T. J. Am. Chem. Soc. 1983, 105, 5706. (b) Sogah, D., Hertler, W., Webster, D., and Cohen, G. Macromolecules 1988, 20, 1473. FNT .sup.3 Lochmann, L., Muller, A. Makromol. Chem. 1990, 191, 1657. FNT .sup.4 Teyssie, P., Fayt, R., Hautekeer, J., Jacobs, C., Jerome, R., Leemans, L., Varshney, S. Makromol. Chem., Macromol. Symp. 1990, 32, 61. (b) Wang, J., Jerome, R., Teyssie, P. Macromolecules 1994, 27, 4902.
Other polymerization systems, such as Catalytic Chain Transfer Polymerization,.sup.1 "Living" Free Radical Polymerization,.sup.1,5 "Metal-free,".sup.6 "Coordination,".sup.7 "Screened,".sup.8 "High-Speed Immortal,".sup.9 and Crown Ether-Promoted.sup.4a,10 anionic polymerizations have been successful to varying degrees in producing narrow MWD PMMA at ambient temperatures. Typically, anionic polymerization of MMA is conducted using bulky, delocalized carbanions as initiators, in polar solvents such as tetrahydrofuran (THF) at low temperatures (i.e., -78.degree. C.) to prevent nucleophilic attack of the carbanion initiator at the carbonyl carbon atom of the ester group of the monomer or polymer. FNT .sup.1 Davis, T., Haddleton, D., Richards, S. J.M.S.-Rev. Macromol. Chem. Phys. 1994, C34, 243. FNT .sup.5 (a) Otsu, T. and Tazaki, T. Polym. Bull. 1986, 16, 277. (b) Georges, M., Veregin, R., Kazmaier, P., Hamer, G. Macromolecules 1993, 26, 2987. (c) Druliner, J. Macromolecules 1991, 24, 6079. (d) Madare, D. and Matyjaszewski. Polymer Preprints (Am. Chem. Soc., Div. Polym. Chem.) 1993, 34, 566). FNT .sup.6 (a) Reetz, M., Knauf, T., Minet, U., and Bingel, C. Angew. Chem. Int. Ed. Engl. 1988, 27, 1371. (b) Reetz, M. Angew. Chem. (Advanced Materials) 1988, 100, 1026. (c) Reetz, M., Minet, U., Bingel, C., and Vogdanis, L. Polymer Preprints (Am. Chem. Soc., Div. Polym. Chem.) 1991, 32, 296. (d) Pietzonka, T. and Seebach, D. Angew. Chem. Int. Ed. Engl. 1993, 32, 716. FNT .sup.7 (a) Yasuda, H., Yamamoto, H., Yokota, K., Miyake, S., and Nakamura, A. J. Am. Chem. Soc. 1992, 114, 4908. (b) Yasuda, H., Yamamoto, H., Yamashita, M., Yokota, K., Nakamura, A., Miyake, S., Kai, Y. and Kanehisa, N. Macromolecules 1993, 26, 7134. FNT .sup.8 Ballard, D., Bowles, R., Haddleton, D., Richards, S., Sellens, R., and Twose, D. Macromolecules 1992, 25, 5907. FNT .sup.9 (a) Sugimoto, H., Kuroki, M., Watanabe, T., Kawamura, C., Aida, T., and Inoue, S. Macromolecules 1993, 26, 3403. (b) Akatsuka, M., Aida, T., and Inoue, S. Macromolecules 1994, 27, 2820. FNT .sup.4 Teyssie, P., Fayt, R., Hautekeer, J., Jacobs, C., Jerome, R., Leemans, L., Varshney, S. Makromol. Chem., Macromol. Symp. 1990, 32, 61. (b) Wang, J., Jerome, R., Teyssie, P. Macromolecules 1994, 27, 4902. FNT .sup.10 (a) Varshney, S., Jerome, R., Bayard, P., Jacobs, C., Fayt, R., and Teyssie, P. Macromolecules 1992, 25, 4457. (b) Wang, J., Jerome, R., Bayard, P., Baylac, L., Patin, M., and Teyssie, P. Macromolecules 1994, 27, 4615.
Other organic cations such as trisdimethylaminosulfonium (TAS.sup.+) have been found to be effective in related polymerization systems..sup.2,11 The n-Bu.sub.4 N.sup.+ salt of 9-methylfluorenyl anion in THF at ambient temperatures produces PMMA with a relatively narrow MWD (2.0), but at low yields (14%)..sup.12 FNT .sup.2. (a) Webster, O., Hertler, W., Sogah, D., Farnham, W., and RajanBabu, T. J. Am. Chem. Soc. 1983, 105, 5706. (b) Sogah, D., Hertler, W., Webster, D., and Cohen, G. Macromolecules 1988, 20, 1473. FNT .sup.11 (a) Starks, C. and Liotta, C. Phase Transfer Catalysis; Academic Press; New York; 1978. (b) Dehmlow, E. and Dehmlow, S. Phase Transfer Catalysis, 2nd Ed.; Verlag Chemie: Florida; 1983. (c) Weber, W. and Gokel, G. Phase Transfer Catalysis in Organic Synthesis; Springer-Verlag; New York; 1977. (d) Starks, C. (Ed.) Phase Transfer Catalysis; ACS Symposium Series 326; American Chemical Society; Washington, 1987. FNT .sup.12 Quirk, R., and Bidinger, G. Polym. Bull. 1989, 22, 63.
Although Reetz et al have postulated that, in the anionic polymerization of n-butyl acrylate at ambient temperatures using a tetrabutylammonium countercation, the intramolecular Claisen type termination reaction is decreased because the electrostatic attraction between the alkoxide and the bulky n-Bu.sub.4 N.sup.+ cation is weak, thereby thermodynamically and kinetically disfavoring the formation of the termination by-product tetrabutylammonium alkoxide..sup.6 Intramolecular cation coordination to the ante-penultimate ester carbonyl group is believed to catalyze the Claisen reaction in the case of alkali metal cations..sup.13 However, anionic polymerizations with ammonium countercations also suffer from some drawbacks, such as low yield, which may be the result of a Hoffmann elimination of a .beta.-hydrogen from the ammonium cation at a rate competitive with polymerization. FNT .sup.6 (a) Reetz, M., Knauf, T., Minet, U., and Bingel, C. Angew. Chem. Int. Ed. Engl. 1988, 27, 1371. (b) Reetz, M. Angew. Chem. (Advanced Materials) 1988, 100, 1026. (c) Reetz, M., Minet, U., Bingel, C., and Vogdanis, L. Polymer Preprints (Am. Chem. Soc., Div. Polym. Chem.) 1991, 32, 296. (d) Pietzonka, T. and Seebach, D. Angew. Chem. Int. Ed. Engl. 1993, 32, 716. FNT .sup.13 (a) Schreiber, H. Makromol. Chem. 1950, 36, 86. (b) Goode, W., Owens, F., Myers, W. J. Polym. Sci. 1960, 47, 75. (c) Lochmann, L., Trekoval, J. Makromol. Chem. 1984, 185, 1819. (d) Gerner, F., Hocker, H., Muller, A., Schulz, G. Eur. Polym. J. 1984, 20, 349.
Thus, a need exists for a method for producing poly(meth)acrylate polymers and copolymers having a narrow molecular weight distribution (so-called "monodisperse" polymers), which provides effective control of (co)polymer molecular weight, of molecular weight distribution and of (co)polymer stereoregularity, in good yields and at ambient temperatures.